Fuel injection device for internal combustion engines

ABSTRACT

A fuel injection system for internal combustion engines, having a high-pressure fuel pump which fills a high-pressure collection chamber with high fuel pressure. Injection lines lead away from the high pressure collection chamber to the individual injection valves. A prefeed pump that feeds fuel from a tank via a low-pressure line system into a work chamber of the high-pressure pump, and at least one control valve controls the high-pressure pumping quantity of the high-pressure pump. Control valves are inserted into the low-pressure line system that adjust the fuel filling flow into the work chamber of the high-pressure pump to the fill volume actually required for operation.

PRIOR ART

The invention is based on a fuel injection system for internalcombustion engines as. In one such fuel injection system for internalcombustion engines, known from the professional journal “mot”, No. 13(1997), Jun. 7, 1997, page 62, a high-pressure pump fills ahigh-pressure collection chamber (common rail) with fuel at highpressure from a tank. From this high-pressure collection chamber, whichis preferably formed by a distributor strip, all the injection lineslead away to the individual injection valves. The high-pressure fuelpump is supplied with fuel from a fuel tank by means of a prefeed pump,which via a low-pressure line system pumps into a work chamber of thehigh-pressure pump. In the known fuel injection system, a control valveis inserted into the low-pressure line system to control thehigh-pressure pumping quantity of the high-pressure pump. This controlvalve controls the flow from a low-pressure feed line into the workchamber of the high-pressure pump, and a high-pressure line leads awayfrom the pump side of this feed line to the high-pressure collectionchamber. Adjusting the high-pressure pumping quantity at thehigh-pressure feed pump is now done by closing the overflow crosssection between the part of the line leading away from the pump workchamber into the low-pressure line system during the pumping strokephase of the high-pressure feed pump. The prefeed pump uninterruptedlysupplies the pump work chamber with fuel, and the fuel first passesthrough the control valve in the low-pressure line system. At the onsetof the pumping stroke motion of the high-pressure feed pump, the controlvalve remains open, so that initially some of the fuel located in thepump work chamber is forced back into the low-pressure line system. Ifhigh-pressure pumping is to be done at the high-pressure pump, thecontrol valve closes the overflow cross section into the low-pressureline system, so that in the further course of the pumping stroke motionof the high-pressure pump, a high fuel pressure is then built up in thepump work chamber and is carried on into the high-pressure collectionchamber via the pressure line. The control of the high-pressure pumpingquantity is effected via the instant of closure of the overflow crosssection from the pump work chamber into the low-pressure operatingsystem by means of the control valve; the high-pressure pumping quantitydecreases, the later the control valve closes this overflow crosssection, and vice versa.

The known fuel injection system for internal combustion engines has thedisadvantage, however, that the entire fuel quantity pumped by theprefeed pump first flows into the work chamber of the high-pressurepump, and then at least some of it is positively displaced back into thelow-pressure line system. In this initial expulsion of the fuel from thework chamber of the high-pressure pump, an unnecessary mass motion offuel takes place, which unnecessarily lessens the efficiency of thehigh-pressure feed pump.

ADVANTAGES OF THE INVENTION

The fuel injection system for internal combustion engines according tothe invention has the advantage over the prior art that the prefeed pumpactually fills the pump work chamber of the high-pressure feed pump withonly the fuel quantity needed at that moment, so that an unnecessaryadditional positive displacement work on the part of the pump pistons ofthe high-pressure feed pump can be avoided. This pumping flow fillingcontrol of the pump work chamber of the high-pressure feed pump asneeded is achieved in a structurally simple way via control means in thelow-pressure circuit filled by the prefeed pump. The low-pressurecircuit is advantageously divided, in a first exemplary embodiment, intothree branches which are jointly filled with fuel by the prefeed pump,preferably embodied as an electric fuel feed pump. A first branch isformed by a feed line to the pump work chamber of the high-pressure feedpump, into which line a constant pressure regulating valve is inserted.A second branch forms a lubricant oil line, which flows through adriving gear chamber of the pump drive of the high-pressure feed pumpand in the process lubricates and cools the pump. This lubricant oilline preferably has a return flow throttle restriction downstream of thepump driving gear and discharges into the tank via a return line thatforms the third branch. An electric pressure control valve, preferably amagnet valve, is intended into this return line into the tank. Thiselectric pressure control valve in cooperation with the constantpressure valve in the feed line to the high-pressure pump forms thecontrol means by way of which the degree of filling of the pump workchamber of the high-pressure pump can be adjusted. The holding pressureor minimum opening pressure of the electric pressure control valve inthe return line is embodied as less than the opening pressure of theconstant pressure valve in the feed line to the high-pressure pump andat the same time is greater than the flow resistance in the lubricantoil line. In this way, a reliable flow through the lubricant oil lineand thus reliable cooling and lubrication of the pump driving gear areassured. In FIG. 2, a further advantageous exemplary embodiment isshown, in which the low-pressure circuit has only two branches. Herepart of the feed line into the pump work chamber of the high-pressurefeed pump forms the lubricant oil line through the pump driving gear.The electric pressure control valve is inserted into the feed linebetween the pump driving gear and the pump work chamber. The mechanicalconstant pressure valve required to set a certain standard pressure isinserted into the return line into the tank. A further advantage isattained by the additional provision of a bypass line between the feedside of the prefeed pump and the high-pressure collection chamber, intowhich line a check valve opening in the direction of the high-pressurecollection chamber is inserted. In this way, when the engine to besupplied is started, a rapid pressure buildup in the high-pressurecollection chamber is attained, and the injection pressure in thehigh-pressure collection chamber can be set to the maximum availablevalue from the prefeed pump. In order to prevent flow losses via thelubricant oil line, it is advantageous to dispose a so-called flowlimiter in series with the throttle restriction in the lubricant oilline; beyond a certain maximum flow, the flow limiter breaks theconnection with the tank. For rapid pressure relief of the fuelinjection system after the engine is turned off, it is furthermoreadvantageous to provide a 2/2-way magnet control valve in a relief lineof the high-pressure collection chamber that discharges into the tank.Via a throttle upstream of this valve, the pressure can also be rapidlydecreased when the control valve is open. In systems with variableinjection pressure, a rapid adaptation to a lower pressure level is alsopossible. In order to avert the risk of overheating of the high-pressurepump, which exists because of the low pumping flow at high ambienttemperatures and low injection quantities or high-pressure pumpingquantities, the control valve in the relief line of the high-pressurecollection chamber is opened purposefully during the pauses betweeninjections if the ambient or fuel temperature exceeds a predeterminedvalue. The resultant increase in the pumping flow into the pump workchamber of the high-pressure pump then assures sufficient cooling of thehigh-pressure pump.

Further advantages and advantageous features of the subject of theinvention can be learned from the description, drawing and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Three exemplary embodiments of the fuel injection system of theinvention are shown in the drawings and will be described in furtherdetail below.

FIG. 1 shows a simplified basic sketch of a first exemplary embodiment,in which the low-pressure circuit has three branches;

FIG. 2 shows a second exemplary embodiment, in which the low-pressurecircuit has two branches; and

FIG. 3 shows a third exemplary embodiment, analogous to FIG. 1, in whichin addition a bypass line is provided between the prefeed pump and thehigh-pressure collection chamber.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The first exemplary embodiment, schematically shown in FIG. 1, of thefuel injection system according to the invention has a high-pressurefuel pump 1, in which an axially reciprocatingly driven pump piston 3,with its end face, defines a pump work chamber 5. Leading away from thispump work chamber 5 is an injection line 7, which on the other enddischarges into a high-pressure collection chamber 9; an outlet checkvalve 11 opening in the direction of the high-pressure collectionchamber 9 is inserted into the injection line 7. From the high-pressurecollection chamber (common rail distributor strip), injection lines 13lead away to the individual injection valves 15. These injection valvescan discharge either directly into the combustion chambers of theindividual cylinders of the engine to be supplied, or alternatively intothe intake conduits of these cylinders.

For fuel supplied by the high-pressure feed pump 1, a low-pressureprefeed pump 17 is also provided, which pumps fuel out of a tank 21 viaan intake line 19. The prefeed pump 17 pumps on the pressure side into alow-pressure circuit, which in the first exemplary embodiment has threebranch lines that can be filled jointly with fuel by the prefeed pump17. A first branch forms a feed line 23 to the high-pressure pump 1 anddischarges there into the pump work chamber 5. A mechanically adjustableconstant pressure valve 25 is inserted into this feed line 23, and inaddition an inlet check valve 27 is inserted at the discharge point intothe pump work chamber 5. A second branch from the feed side of theprefeed pump 7 forms a lubricant oil line 29, which flows through adriving gear 31, preferably a piston drive, that drives thehigh-pressure pump 1. After emerging from the driving gear 31, thelubricant oil line 29 (coolant oil line) discharges into the tank 21,and a return throttle restriction 33 is provided in the lubricant oilline 29 downstream of the driving gear 31. A third branch of thelow-pressure line system is formed by a return line 35, which dischargesjointly with the lubricant oil line 29 into the tank 21, and into whichan electrically triggerable pressure control valve 37 is inserted. Thispressure control valve 37 is preferably embodied as amagnet-valve-controlled control valve.

For monitoring the pressure in the high-pressure collection chamber 9, apressure 39 can also be provided there. A fuel filter 41 is alsoinserted into the low-pressure line system, preferably near thefeed-side exit from the prefeed pump 17.

The first exemplary embodiment of the fuel injection system of theinvention functions as follows. With the onset of operation of theengine to be supplied, the prefeed pump 17 makes the volumetric flowrequired to operate the high-pressure feed pump 1 available. To thatend, the prefeed pump 17 pumps fuel out of the tank 21 via the intakeline 19 into the individual partial lines 23, 29 and 35 of thelow-pressure line system. The minimum holding pressure or minimumopening pressure of the electric control valve 37 in the return line 35is designed such that in the currentless state, a predetermined pressure(preferably approximately 0.3 bar) still drops so as to assure a minimumflow through the lubricant oil line 29 and the driving gear 31. Thislubricating oil or coolant pumping flow in the lubricant oil line 29 forthe pump driving gear 31 is determined by the pilot pressure built upand by the cross section of the return throttle 33. The opening pressureof the constant pressure valve 25 in the feed line 23 is above theminimum holding pressure of the electric control valve 37.

Alternatively, the elevated opening pressure of the constant pressurevalve 25 can also be achieved directly in the inlet valve 27 of thehigh-pressure pump 1. Using the additional pressure valve 25 isespecially advantageous whenever filling differences in a multipistonpump are to be avoided, differences that can be caused by tolerances inthe opening pressure of the inlet valves.

In partial-load engine operation, the pilot pressure in the low-pressurecircuit is now set, via the electrically adjustable pressure controlvalve 37, in such a way that in accordance with the pressure differenceat the constant pressure valve 25 (an opening pressure preferably ofapproximately 0.5 bar), precisely the fuel quantity required forinjection can pass through and flows into the pump work chamber 5. Theopening pressure of the inlet check valve 27 is below the openingpressure of the db 25. The fuel quantity that flows into the pump workchamber 5 of the high-pressure pump 1 during the interval betweeninjections is now compressed during the pumping stroke in the directionof top dead center of the pump piston. 3, and once a certain injectionpressure value is exceeded, it flows over, via the outlet check valve11, into the high-pressure collection chamber 9. There, the high fuelpressure is propagated via the injection lines 13 to the respectiveinjection valves 15, where it is brought to injection in a known,controlled manner.

The fuel vapor that occurs during the intake phase because of thenegative quantitative balance in the pump work chamber 5 in thepartial-load range is recondensed in the ensuing pumping stroke of thepump piston 3. By setting a defined opening pressure at the inlet checkvalve 27 of the high-pressure pump 1, it is assured that the creation offuel vapor remains limited to the pump work chamber 5, which guaranteesa replicable pumping flow of the high-pressure pump 1. If the injectionquantity at the injection valves 15, and thus the high-pressure fuelquantity to be pumped by the high-pressure pump 1, is to be increased,then the opening pressure at the electric pressure control valve isincreased accordingly, so that a larger pumping quantity from theprefeed pump 17 reaches the pump work chamber 5 of the high-pressurepump 1 via the feed line 23. The return throttle 33 prevents anuncontrolled outflow of pumped fuel via the lubricant oil line 29. Thepumping quantity pumped into the pump work chamber 5 can thus beadjusted individually from one injection to another via the openingpressure of the electric pressure control valve 37, as a function of theopening pressure of the pressure valve 25.

The second exemplary embodiment, shown in FIG. 2, of the fuel injectionsystem for internal combustion engines of the invention differs from thefirst exemplary embodiment in the embodiment of the low-pressure linesystem, which now has only two branches leading away from the prefeedpump 17. One branch is again formed by a return line 35 into the tank21, and a constant pressure valve 125 is now inserted into this returnline 35. The second branch is formed by the feed line 23 to thehigh-pressure pump 1, and the feed line 23 flows through the drivinggear 31 of the high-pressure pump 1 and thus jointly acts as part of theoriginal lubricant oil line. An electric pressure control valve 137 isinserted between the driving gear 31 and the pump work chamber 5 of thehigh-pressure pump 1, and it is adjoined, shortly before the dischargepoint of the feed line 23 into the pump work chamber 5, by an internalcombustion engine 27 that opens in the direction of the pump workchamber 5.

The function of the second exemplary embodiment is analogous to thefirst exemplary embodiment; the control of filling of the pump workchamber 5 is again effected via the electric pressure control valve 137as a function of the differential opening pressure of the pressure valve125, in such a way that only the quantity of fuel required at thatmoment is fed into the pump work chamber 5. The excess fuel quantitypumped by the prefeed pump 17 is returned to the tank 21 via the returnline 35. This system, without a return line from the pump driving gear31 to the tank, is preferably suitable for use in direct-injectioninternal combustion engines with externally supplied ignition, so as toprevent any additional heating of the tank volume and thus an increasedload on the tank venting system.

The third exemplary embodiment, shown in FIG. 3, of the fuel injectionsystem for internal combustion engines according to the invention hasthe same basic layout as the first exemplary embodiment described inFIG. 1 and is merely expanded with two further functions. The fuelinjection system of FIG. 3 has an additional bypass line 43, whichbeginning at the pumping pressure side region of the low-pressure linesystem discharges into the high-pressure collection chamber 9. A checkvalve 45 opening in the direction of the high-pressure collectionchamber 9 is inserted into this bypass line 43. The bypass line 43 makesit possible to fill the high-pressure collection chamber 9 directly bythe prefeed pump 17, so that when the engine to be supplied is started,the injection pressure in the high-pressure collection chamber 9 can bebuilt up very quickly to the maximum available pressure value from theprefeed pump 17. This is advantageous in injection systems for internalcombustion engines with externally supplied ignition, since when theengine is started, the pressure buildup in the high-pressure collectionchamber 9 can be delayed by inclusions of gas or air in thehigh-pressure circuit. The injection pressure required for injection cannow be adjusted very quickly to the maximum available value from theprefeed pump 17. To make it possible to avoid flow losses via thelubricant oil line 29, it is advantageous to dispose a flow limitingvalve 47 (or flow limiter) in the lubricant oil line 29, in series withthe return throttle 33; beyond a certain flow value, this flow limiterbreaks the connections with the tank 21.

The third exemplary embodiment shown in FIG. 3, in a supplement to thefirst exemplary embodiment shown in FIG. 1, also has an additionalrelief line 29 of the high-pressure collection chamber 9, and this linedischarges into a tank 21. An electrically triggerable 2/2-way controlvalve 51, preceded in the flow direction by a throttle restriction 53,is inserted into this relief line 49. Thus via this relief line 49, thepressure in the high-pressure collection chamber 9 can advantageously bedecreased quickly after the engine is turned off. Furthermore,particularly in injection systems with variable injection pressure, arapid adaptation of the pressure in the high-pressure collection chamber9 to a lower pressure level is possible. In order at high ambienttemperatures and low injection quantities to counteract the risk thatthe high-pressure feed pump 1 will run hot because of the small pumpingflow quantities, the 2/2-way control valve 51 can open the relief lineduring the intervals between injection if the ambient or fueltemperature exceeds a predetermined value. The increase, resulting fromthis pressure relief in the high-pressure collection chamber 9, in thefilling pumping flow into the pump work chamber 5 of the high-pressurepump 1 makes additional cooling of the high-pressure pump 1 possible.The 2/2-way valve 51, embodied as a magnet valve, is switched such thatin its currentless state, the flow cross section to the tank 21 isopened up.

With the fuel injection system for internal combustion engines of theinvention, it is thus possible, by suitable control in the low-pressureline system, to adjust the degree of filling of the pump work chamber 5of the high-pressure pump 1 to the fuel volume actually needed at thatmoment, so that excessive positive displacement work on the part of thehigh-pressure pump 1 can be avoided. The fuel injection system of theinvention is suitable for supplying both internal combustion engineswith externally supplied ignition and self-igniting internal combustionengines.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

What is claimed is:
 1. A fuel injection system for internal combustionengines, comprising a high-pressure fuel pump (1) which fills ahigh-pressure collection chamber (9) with high fuel pressure, from thehigh-pressure collection chamber, injection lines (13) lead away fromthe collection chamber to individual injection valves (15), a prefeedpump (17) that pumps fuel from a tank (21) via a low-pressure linesystem into a work chamber (5) of the high-pressure pump (1), at leastone control valve for controlling the high-pressure pumping quantity ofthe high-pressure pump (1), adjustable constant pressure valve means(25) is inserted into the low-pressure line system that adjust the fuelfilling flow into the work chamber (5) of the high-pressure pump (1) tothe fill volume required for operation.
 2. The fuel injection systemaccording to claim 1, in which the low-pressure line system has threebranches, each of said three branches are filled jointly by the prefeedpump (17), of which a first branch forms a feed line (23) to thehigh-pressure pump (1), a second branch forms a lubricant oil line (29)into the driving gear (31) that drives the high-pressure pump (1), and athird branch forms a return line (35) into the tank (21), and thelubricant oil line (29), after emerging from the driving gear (31),discharges into the tank (21).
 3. The fuel injection system according toclaim 2, in which an electric pressure control valve (37) is insertedinto the return line (35), and at least one further pressure valve (25)is inserted into the feed line (23) to the high-pressure pump (1), andthese valves form the control means for filling the work chamber (5) ofthe high-pressure pump (1).
 4. The fuel injection system according toclaim 3, in which the pressure valve (25) in the feed line (23) isembodied as a constant pressure valve.
 5. The fuel injection systemaccording to claim 3, in which a further pressure valve is inserted intothe feed line (23), preferably near the discharge point into the workchamber (5) of the high-pressure pump (1), and is embodied as a checkvalve (27) that opens in the direction of the high-pressure pump (1). 6.The fuel injection system according to claim 2, in which the lubricantoil line (29) has a throttle restriction (33) downstream of the pumpdriving gear (31).
 7. The fuel injection system according to claim 3, inwhich the lubricant oil line (29) discharges into the return line (35)downstream of the electric pressure control valve (37).
 8. The fuelinjection system according to claim 2, in which a high-pressure line (7)leads away from the work chamber (5) of the high-pressure pump (1), anddischarges into the high-pressure collection chamber (9), and a checkvalve (11) opening in the direction of the high-pressure collectionchamber (9) is inserted into said high-pressure collection line.
 9. Thefuel injection system according to claim 3, in which the openingpressure of the pressure valve (25) in the feed line (23) to thehigh-pressure pump (1) is greater than the minimum opening pressure ofthe electric pressure control valve (37).
 10. The fuel injection systemaccording to claim 3, in which the minimum opening pressure of theelectric pressure control valve (37) is greater than the flow resistancein the lubricant oil line (29).
 11. The fuel injection system accordingto claim 1, in which the low-pressure line system has two branchesfilled jointly by the prefeed pump (17), of which a first branch forms afeed line (23) to the high-pressure pump (1) and a second branch forms areturn line (35) into the tank (21).
 12. The fuel injection systemaccording to claim 11, in which the feed line (23) flows through adriving gear (31) that drives the high-pressure pump (1).
 13. The fuelinjection system according to claim 12, in which an electric pressurecontrol valve (137) is inserted into the feed line (23) between the pumpdriving gear (31) and the discharge point of the feed line (23) into thework chamber (5) of the high-pressure pump (1).
 14. The fuel injectionsystem according to claim 13, in which a check valve (27) opening in thedirection of the work chamber (5) of the high-pressure pump (1) isinserted into the feed line between the electric pressure control valve(137) and the discharge point into the work chamber (5) of thehigh-pressure pump (1).
 15. The fuel injection system according to claim11, in which a pressure valve (125) is inserted into the return line(35).
 16. The fuel injection system according to claim 2, in which anadditional bypass line (43) is provided between the feed side of theprefeed pump (17) and the high-pressure collection chamber (9), a checkvalve (45) opening in the direction of the high-pressure collectionchamber (9) is inserted into said bypass line.
 17. The fuel injectionsystem according to claim 11, in which an additional bypass line (43) isprovided between the feed side of the prefeed pump (17) and thehigh-pressure collection chamber (9), a check valve (45) opening in thedirection of the high-pressure collection chamber (9) is inserted intosaid bypass line.
 18. The fuel injection system according to claim 1, inwhich a relief line (49) leads away from the high-pressure collectionchamber (9) into the tank (21), and an electric control valve (51) isinserted into said relief line (49).
 19. The fuel injection systemaccording to claim 18, in which the electric control valve (51) of therelief line (49) is preceded in the flow direction by a throttlerestriction (53).
 20. The fuel injection system according to claim 1, inwhich a fuel filter (41) is inserted into the low-pressure line system,near an exit from the prefeed pump (17).